Although the vast majority of US research on trends in the inequality of family income is based on public-use March Current Population Survey (CPS) data, a new wave of research based on Internal Revenue Service (IRS) tax return data reports substantially higher levels of inequality and faster...

Recent research on United States levels and trends in income inequality vary substantially in how they measure income. Piketty and Saez (2003) examine market income of tax units based on IRS tax return data, DeNavas-Walt, Proctor, and Smith (2012) and most CPS-based research uses pre-tax,...

Access to IRS personal income tax records improves researchers' ability to track U.S. income and inequality, especially at the very top of the distribution (Piketty and Saez 2003). However, rather than following standard Haig-Simons income definitions, tax form income measures were designed to...